New Pluto Photos Contain Multitude of Mysteries

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Scientists are stunned at the incredible new images of the
surface of Pluto, its largest moon Charon and its farthest-flung
moon Hydra, which are just the tip of the scientific iceberg that
will be sent back by NASA's New Horizons probe in the wake of its
epic flyby.

New Horizons made its
closest approach to Pluto at 7:49 a.m. (1149 GMT) Tuesday
morning (July 14), but it took almost 24 hours for scientists to
get a sneak peek at the treasure trove of data that the probe
picked up. It will take 16 months for the spacecraft to beam home
the entire volume of information it collected during its historic
Pluto encounter.

At a media briefing held today (July 15), leaders of the New
Horizons team discussed some of the new images taken during and
around closest approach. Among other amazing revelations, the new
photos showed that Pluto's surface is surprisingly young and is
studded with big, icy mountains; and that Charon has been
geologically active recently and possesses canyons up to 6 miles
(10 kilometers) deep. [ New
Horizons Probe's July 14 Pluto Flyby: Complete Coverage ]

The image of
Pluto's most distant moon, Hydra, may look like little more
than a pixelated blob, but the clever scientists with New
Horizons have used that image to finally determine the size of
the elongated satellite — 28 miles by 19 miles (45 by 31 km).

"Prior to New Horizons' revealing of Hydra, we were completely
uncertain about how big [it] was," New Horizons project scientist
Hal Weaver, of the Johns Hopkins University Applied Physics
Laboratory in Laurel, Maryland, said at today's media briefing.
"It could have been anywhere from 20 miles [32 km] across to 100
miles [160 km] across."

Weaver said the image shows that Hydra reflects about 45 percent
of the sunlight that hits it, and "that can only mean that
Hydra's surface is probably composed primarily of water ice. It's
the only way to get it that bright. And that's cool."

Weaver said there are more images of Hydra coming soon, which
will be two to three times sharper than the image released today.

"I originally thought Charon might be an ancient terrain covered
in craters," said New Horizons deputy project scientist Cathy
Olkin, of the Southwest Research Institute (SwRI) in Boulder,
Colorado. "Many people on the team thought that might have been
the case. And Charon just blew our socks off."

The stunning array of features found on Charon
may be even more surprising than those found on Pluto. In the
new image, on the upper right edge of the satellite (at about the
2 o'clock position), there appears to be a chunk of material
chiseled out of Charon's side. That is actually a canyon that
scientists think is anywhere from 4 to 6 miles (6.4 to 10 km)
deep. (Earth's Grand Canyon is just over 1 mile, or 1.6 km,
deep.) A second canyon on the upper left side is approximately 3
miles (4.8 km) deep.

At Charon's northern pole is a
noticeably dark region that Olkin said the team has been
(unofficially) referring to as "Mordor." But the dark region
might only be a thin veneer over the surface, she said. Near the
center of "Mordor," the image reveals a few bright spots that
appear to be craters. It's possible meteorites hit Mordor,
blasting the dark material away and revealing brighter stuff
beneath. The reddish spray of material surrounding the dark
region could lend more support to that theory, Olkin said.

"That's just striking to me. It's amazing to see this," Olkin
said. "This is a huge area, and it could be that it's due to
internal processing, and we will be looking at that in more
detail."

Below the strip of cliffs and troughs is a smooth region, with
very few craters.
Earth's moon is covered in craters because it has been
pummeled by meteorites for 4.5 billion years. Only a surface that
is relatively young — that has been refreshed through geologic
turnover — would lack craters.

Olkin said it's possible this region of Charon's surface is
geologically active. New Horizons principal investigator Alan
Stern, also of SwRI, said this was a big surprise.

"So we've been saying
Pluto did not disappoint," Olkin said. "I can add that Charon
did not disappoint, either."

The close-up image of Pluto's entire face that was released
Monday (July 14) wowed the world, but today the New Horizons
team unveiled a small segment of a mosaic image that shows the
surface in much greater detail.

The frame covers a region about 150 miles (240 km) wide and
features resolution down to 0.5 miles (0.8 km), according to New
Horizons scientist John Spencer, also of SwRI.

According to a statement from NASA, the image was taken 1.5 hours
before New Horizons' closest approach to Pluto, when the craft
was 47,800 miles (77,000 kilometers) from the surface of the
planet.

"There's a region that looks sort of hillocky and a region that
looks like a fault," Spencer said. "And that terrain down towards
the lower right looks really strange. It's like … piles of stuff
with grooves on it.

"And then we have smooth flowing plains filling in some of the
low spots," he added. "There's been erosion, there's been
mountain-building, there's been whatever produces lumpy terrain
with grooves on it. And it's baffling. It's baffling in a very
interesting and wonderful way. And I hope that when we get more
context and we can fill in how this fits in with the rest of the
geology,
it'll start to make some sense. We can only hope."

According to Spencer, the mountains New Horizons spotted on Pluto
reach heights of 11,000 feet (3,500 m) above the surface, and
there "may be higher ones elsewhere." (The highest peaks in the
Rocky Mountains are around 14,000 feet, or 4,200 m).

"We know the surface
of Pluto is covered in a lot of nitrogen ice, methane ice,
carbon monoxide ice," Spencer said. "You can't make mountains out
of that stuff. It's just too soft, it doesn't have the strength
to make mountains on Pluto."

The researchers therefore theorize that the mountains must be
supported on a bedrock of water ice, which, at the cold
temperatures on Pluto's surface, is hard enough to form tall
mountains.

"So the nitrogen and the methane are just a coating on top of
this icy bedrock," Spencer said.

But even more surprising than the presence of mountains on the
dwarf planet's surface was the lack of craters.

"Pluto is being bombarded by other Kuiper Belt
objects — craters happen," Spencer said. The smooth terrain
implies that the dwarf planet has been geologically active quite
recently.

"Just eyeballing it, we think it has to be probably less than 100
million years old," he added. "It might be active right now.
Without craters you just can't put a lower limit on how active it
might be."

In a
statement from NASA released shortly after the media
briefing, Jeff Moore, leader of New Horizons' geology, geophysics
and imaging team, said the surface appears to be "one of the
youngest surfaces we’ve ever seen in the solar system."

Geologic activity has to be driven by an energy source. In the
geologically active icy moons that orbit Saturn and Jupiter,
scientists "usually attribute this to tidal heating, or
deformation of these worlds by the gravity of that giant planet
and interactions with other moons," Spencer said. "That can't
happen on Pluto, because there is no giant body that can deform
it on a regular basis. This is telling us that you do not need
tidal heating to power geologic activity on icy moons. That's a
really important discovery that we just made this morning."

Spencer said more frames from the high-resolution mosaic image of
Pluto's surface will be released on Friday (July 17), and that
those will "show equally amazing things I'm sure. So stay tuned."